It is generally known that permanent waving is carried out in two steps, the reductive splitting of the cysteine disulfide bonds in the hair by a reducing agent, and the subsequent neutralization by application of an oxidizing agent, whereby the cysteine disulfide bonds are restored.
The reducing agent still most frequently used today is thioglycolic acid, also in form of the salts thereof, in particular its ammonium salt, although numerous other thio compounds have been proposed for this purpose, which, however, mostly did not succeed.
The compositions containing thioglycollates are customarily applied at a pH-value between 7 and 10, in particular 8.5 and 9.5.
Such compositions vary in their waving and/or straightening performance and, therefore, there is still need for further improvement.